As is well-known, control over various types of vehicle equipment is exercised on a vehicle, including control over fuel injection of a vehicle engine. In the case of the control over vehicle engine fuel injection, the air-fuel ratio of a mixture for combustion is recognized each time the mixture is supplied based on a signal output by an oxygen sensor for detecting the concentration of oxygen in the exhaust pipe. The amount of fuel injection is controlled according to the recognition (the mixture is recognized to be rich or lean) to reduce the amount of harmful substances included in the exhaust gas. However, such control may adversely affect engine output and may even increase the amount of harmful substances included in the exhaust gas against what is intended when proper control over the fuel injection amount is disabled by, for example, an abnormality of the oxygen sensor.
It is therefore proposed to provide a vehicle with a vehicle abnormality monitoring apparatus for monitoring abnormalities of various vehicle equipment including a vehicle engine. Specifically, such a vehicle abnormality monitoring apparatus monitors abnormalities of vehicle equipment based on, for example, a signal output by a sensor for detecting a physical quantity which varies depending on the operating status of the vehicle equipment. When an abnormality of the sensor or another type of vehicle equipment is detected, the vehicle abnormality monitoring apparatus stores and holds in a data memory an abnormality code associated with the abnormality or monitoring data such as freeze frame data that is data indicating the operating status of the vehicle equipment at the time when the abnormality of the vehicle equipment is detected. In addition, a fail-safe function set in advance in association with the abnormality code thus stored and maintained is executed, and other control units are instructed to execute the same fail-safe function. The freeze frame data among data stored in the data memory is normally output from the data memory to an external tool through wire communication and used to analyze the cause of the abnormality of the vehicle equipment when the vehicle equipment is repaired or inspected.
In order to satisfy recent requirements associated with environmental preservation and safety of vehicles, control is frequently exercised to compensate for fluctuating physical characteristics. Examples of such control include control over the fuel injection of a vehicle engine as described above and control over the brake of a vehicle. Types and quantity of vehicle equipment provided for exercising such control are on the increase year after year, such equipment including oxygen sensors for detecting the concentration of oxygen in an exhaust pipe and vehicle speed sensors for detecting the traveling speed of a vehicle. That is, in a vehicle diagnosis apparatus, types and amount of monitoring data to be stored in the data memory are increasing, and it may become difficult to properly store and hold the monitoring data depending on the capacity of the data memory.
Under the circumference, proposals are made in the a related art, including a vehicle abnormality monitoring apparatus adapted to save (transfer) freeze frame data among monitoring data stored in a data memory in a data storage unit of a management station which is provided outside the vehicle and which transmits and receives information to and from the vehicle abnormality monitoring apparatus through radio communication, as disclosed in U.S. Pat. No. 6,256,594 (JP-11-65645A).
As described above, the freeze frame data is stored and maintained to be used for analyzing the cause of an abnormality of vehicle equipment. In this sense, it is not essential to store and hold such data in the data memory of the vehicle abnormality monitoring apparatus. In this regard, in the vehicle abnormality monitoring apparatus disclosed in U.S. Pat. No. 6,256,594, since the freeze frame data is stored and maintained in the data storage unit of a management station available to many vehicles, the corresponding data in the data memory may be erased.
As thus described, in the case of the vehicle abnormality monitoring apparatus according to the related art, since freeze frame data which has been completely transferred may be erased from the data memory, a greater amount of monitoring data can be stored and maintained (accumulated) in the same data memory.
In the vehicle abnormality monitoring apparatus according to the related art, however, a transfer error can occur when freeze frame data stored in the data memory is transmitted to the management station on a radio communication basis, and such data having an error can consequently be stored in the data storage unit of the management station. In case that the freeze frame data stored and maintained in the data memory is erased in such a situation, the reliability of the freeze frame data itself can be significantly reduced.